Focal length of the lens often has considerable error due to assembly and lens accuracy. Thus when assembly the compact camera module (CCM) of the mobile electronic device such as a phone, one would need rotate the thread to make up and down focus adjustment through the outside outer screw of the lens and the inner screw on the lens voice coil motor (VCM) holder to compensate this focus length error. Usually the mobile phone camera module in the assembly, the voice coil motor is non-energized condition; the lens is rotated for making up and down adjustment until object focal distance (infinity) is corresponded. That is the object focal distance is focused on a surface of a sensor integrated circuit. FIG. 1 illustrates a diagram of conventional focus point for the image of infinity distance. As shown in FIG. 1, image of an object 160 of infinite distance passes through objective lens 150, due to the focus point 110 is set on a surface of a sensor integrated circuit 120, the image is in clear state. Wherein 130 and 140 denote the positive and negative error value when focused, respectively. This error value will cause the image into unclear state. This conventional technique sets the focus point of the lens on the proper position 110 of the surface 120 of the sensor integrated circuit by focusing action.
Furthermore, this structure with screw and thread has the problem of matching the size of the screw, and small particles are generated due to friction when the screw is rotated up and down for focus adjustment, thereby the production yield is affected by this problem.